The conventional gap filler used to protect a space shuttle vehicle from overheating during re-entry in the earth's atmosphere consists of pads made from aluminoborosilicate cloth filled with alumina fibers. The cloth is sewn together in the form of a pillow to hold the refractory fibers. The pad is constructed in several sizes ranging from 0.1 to 0.2 inch in thickness, although its flexibility may allow additional alteration by in situ compression. Its applicability to the vehicle, however, is seriously limited because of the impossibility of fabricating specimens of less than 0.1 thick. The filler pad of the art is installed in the tile gaps and attached by a "velcro" strip fastened to the pad's base, said strip engaging another "velcro" strip clipped under the vehicle tiles. Alternatively, the pad is trapped between tiles by overhangs on adjacent tiles which prevent it from coming out of the gap.
This conventional gap filling system therefore suffers from various shortcomings which may be summarized as follows. Gaps less than 0.1 inch wide cannot be filled, leaving a large number of vulnerable points in the heat shield. The tiles made with overhangs must be designed to accept the filler, thus eliminating the possibility of refilling the gaps when the filler has been damaged. Finally, the low emittance of the conventional filler may cause, in larger gaps, high filler surface temperatures during entry into the atmosphere, a phenomenon which may adversely affect the filler's reusability and the safety of the flight as well.
The primary objective of this invention is to provide a filler which will effectively prevent hot gas flow between heat shield tiles and thus prevent overheating of the underlying aluminum structure of the vehicle, while at the same time allowing sufficient space for thermal expansion and contraction during orbital operations.
Another objective is to provide simple means by which small gaps of various lengths and widths between ceramic tiles of a space vehicle heat shield can be custom fit with a filler without having to remove the surrounding tiles to close said gaps. A further objective is to provide a filler which, if necessary, can be replaced between flights, again without removal of vicinal tiles.